The invention relates to storing a digitized stream of interlaced video image data in a memory in noninterlaced form.
Frames of digitized video data are often stored in a video memory including a random access memory (RAM) and a serial access memory (SAM). The RAM is organized so as to be addressed by column addresses and row addresses, each storage location being identified by a unique combination of a column address and a row address. The locations having the same row address are considered a "page", and within a page, each column address identifies a pixel storage location. The SAM has enough storage for a page, and data can be transferred between the SAM and the RAM. In split video memories, the SAM is divided into a lower SAM (LSAM) that corresponds to lower column addresses and an upper SAM (USAM) that corresponds to upper column addresses. In split memories, transfer can be made between the entire SAM and a page of the RAM at one time, or transfer can be made between the LSAM and corresponding lower column address locations in a page of the RAM or between the USAM and corresponding upper column address locations in a page of the RAM.
In interlaced video, a frame is divided into two fields which are transmitted one after the other; one field contains the even lines of a frame, and the other field contains the odd lines of the frame. When capturing a frame, it is desirable to store the pixel data in noninterlaced form, requiring that pixel data for lines from the second field being received be stored in locations in the memory left between the lines of the first field.
Another consideration that must be addressed in capturing frames is the fact that the length of horizontal lines in a digitized field of pixel data typically is shorter than a page width. One simply cannot continuously write the pixel data into RAM when going from one page to another in the middle of a video line, as pixel data would be lost in the discrete amount of time that is necessary for changing page addresses. If a single line is stored on each page, to avoid loss of data when changing pages during receipt of a line, there is wasted RAM space after each line.
A prior art technique for storing pixel data in a video RAM seamlessly (without gaps) involves using a buffer to temporarily store incoming pixel data before reading into the memory as necessary while changing page boundaries.